1. Field of the Invention
The present invention relates to an image display device capable of changing a wide vision display and narrow vision display, an electronic apparatus using the same, a display output control method for the image display device, and an output control program thereof.
2. Description of the Related Art
Recently, liquid crystal displays (LCDs) are broadly used for display elements of general-use display devices such as mobile phones and notebook personal computers as well as display elements of ATMs (Automatic Teller Machines) and industrial information terminal devices used in convenience stores and the like. Due to the technical developments achieved heretofore, the LCD has no viewing-angle dependency, and the display thereof can be visually recognized from every direction. While the mobile terminals such as the mobile phones and the notebook personal computers are normally used with a wide vision display, there are many opportunities to display personal information and secret information thereon in public places because of their nature as the terminals. Under such circumstances, there is a demand to limit the viewing angle so as not be peeped by others. Further, with ATMs and the information terminal devices placed in convenience stores and the like, the viewing angle of the display elements are limited by providing a viewing-angle limiting film on top of the display elements for the sake of privacy protection and information security.
In the meantime, there is a demand to use such information terminal devices as advertisement media by setting those to a wide viewing angle display when no one is using the devices.
As described, there has been an increasing demand for making it possible to change the viewing angles of the display devices depending on the use conditions thereof regarding various kinds of display devices.
For such demands, Japanese Unexamined Patent Publication Hei 11-231794 (paragraphs [0018]-[0020] (Patent Document 1)), for example, proposes a display technique which is capable of changing viewing angles. This technique will be described hereinafter by referring to FIG. 24. As shown in FIG. 24, a diffusion device 103, luminance enhancement films 104 and 105, a unit 110 formed with a louver film which restricts the spread angles of light, a variable diffusion cell 111, and an LCD screen 106 are placed on a backlight system constituted with a line of fluorescent lights 101 and a mirror 102 in a sequentially stacked manner.
The variable diffusion cell 111 can change a transparent state and a light scattering state by applying or not applying an electric field. As the cell, a polymer dispersed liquid crystal cell or a polymer stabilized cholesteric structure cell can be used. Through changing the transparent state and the light scattering state of the variable diffusion cell 111 electrically, it is possible to change the narrow vision display with which the display can be viewed only from a narrow angle range and the wide vision display with which the display can be recognized from a wide angle range.
Further, as other related techniques, there are Japanese Unexamined Patent Publication 2006-323031 (Patent Documents 2), Japanese Unexamined Patent Publication 2007-233373 (Patent Documents 3), and Japanese Unexamined Patent Publication 2007-298844 (Patent Documents 4).
Among those, Patent Document 2 discloses a display device which includes: a surface light source which emits light on a plane towards the viewer side; a viewing angle control module provided in front of the surface light source for increasing the directivity of transmission light; a changing element provided on the front face of the viewing angle control module, which is adhesively attached via an adhesive layer; and a display panel provided in front of the changing element. Among those, the changing element changes to a transparent state where incident light is transmitted as it is or to a semitransparent opaque state where the incident light is let through by being scattered.
Further, Patent Document 3 discloses a display device capable of changing the viewing angle range, which includes: a light source device that is provided with a transparent-scattering changing element capable of changing a state for transmitting incident light and a state for scattering the incident light; and a transmission-type liquid crystal display panel including pixels for display arranged in matrix, which drives the transparent-scattering changing element by using a power supply and signals for driving the pixels.
Furthermore, Patent Document 4 discloses a display device which is constituted with: a lighting angle variable light source device formed with a backlight functioning as a light source and a light beam control device; and a transmission type display device. The light beam control device is provided with a transparent-scattering element capable of electrically changing straightforward emission and scattering emission of incident light, which is stacked on a light beam control film device.
However, in the variable viewing angle display technique disclosed in Patent Document 1, there is such a shortcoming that no measure is taken for a fault that may occur in changing the viewing angles. That is, there is a possibility of causing leakage of screen information when the screen turns to the wide vision display because of a fault when it is intended to be used as the narrow vision display. Particularly, with the information terminals device such as the ATM where it is important to keep the security of the display information, such fault can become a fatal event that may lose the reliability for the customers.
Further, since there is also no measure for a fault in changing the viewing angles taken in the display devices disclosed in Patent Documents 2, 3, and 4, there is a possibility leaking screen information when the screen turns to the wide vision display because of a fault when it is intended to be used as the narrow vision display.
The present invention is designed in view of such circumstances, and it is an exemplary object of the present invention to provide an image display device which can prevent leakage of information displayed on the display screen even when there is a fault generated in the viewing angle changing function, and to provide an electronic apparatus using the same, a display output control method for the image display device, and an output control program thereof.